For example, rodents who were exposed to cold (an environmental stressor) had impaired memory due to a decline in neurotransmitters (, ).

However, when these rodents were given a tyrosine supplement, the decline in neurotransmitters was reversed and their memory was restored.

While rodent data does not necessarily translate to humans, human studies have found similar results.

In one study in 22 women, tyrosine significantly improved working memory during a mentally demanding task, compared to a placebo. Working memory plays an important role in concentration and following instructions ().

In a similar study, 22 participants were given either a tyrosine supplement or placebo before completing a test used to measure cognitive flexibility. Compared to the placebo, tyrosine was found to improve cognitive flexibility ().

Cognitive flexibility is the ability to switch between tasks or thoughts. The quicker a person can switch tasks, the greater their cognitive flexibility.

Additionally, supplementing with tyrosine has been shown to benefit those who are sleep deprived. A single dose of it helped people who lost a night’s sleep stay alert for three hours longer than they otherwise would ().

Phenylketonuria (PKU) is a rare genetic condition caused by a defect in the gene that helps create the enzyme phenylalanine hydroxylase ().

Your body uses this enzyme to convert phenylalanine into tyrosine, which is used to create neurotransmitters ().

However, without this enzyme, your body cannot break down phenylalanine, causing it to build up in the body.

The primary way to treat PKU is to follow a special diet that limits foods containing phenylalanine ().

However, because tyrosine is made from phenylalanine, people with PKU can become deficient in tyrosine, which can contribute to behavioral problems ().

Supplementing with tyrosine may be a viable option for alleviating these symptoms, but the evidence is mixed.

In one review, researchers investigated the effects of tyrosine supplementation alongside or in place of a phenylalanine-restricted diet on intelligence, growth, nutritional status, mortality rates and quality of life ().

The researchers analyzed two studies including 47 people but found no difference between supplementing with tyrosine and a placebo.

A review of three studies including 56 people also found no significant differences between supplementing with tyrosine and a placebo on the outcomes measured ().

The researchers concluded that no recommendations could be made about whether tyrosine supplements are effective for the treatment of PKU.

Summary PKU is a serious condition that may cause tyrosine deficiency. More studies are needed before recommendations can be made about treating it with tyrosine supplements.

Depression is thought to occur when the neurotransmitters in your brain become unbalanced. Antidepressants are commonly prescribed to help realign and balance them ().

Because tyrosine can increase the production of neurotransmitters, it’s claimed to act as an antidepressant ().

However, early research doesn’t support this claim.

In one study, 65 people with depression received either 100 mg/kg of tyrosine, 2.5 mg/kg of a common antidepressant or a placebo each day for four weeks. Tyrosine was found to have no antidepressant effects ().

Depression is a complex and varied disorder. This is likely why a food supplement like tyrosine is ineffective at combating its symptoms.

Nevertheless, depressed individuals with low levels of dopamine, adrenaline or noradrenaline may benefit from supplementing with tyrosine.

As a supplement, tyrosine is available as a free-form amino acid or N-acetyl L-tyrosine (NALT).

NALT is more water-soluble than its free-form counterpart, but it has a low conversion rate to tyrosine in the body (, ).

This means that you would need a larger dose of NALT than tyrosine to get the same effect, making the free-form the preferred choice.

Tyrosine is commonly taken in doses of 500–2,000 mg 30–60 minutes before exercise, even though its benefits on exercise performance remains inconclusive (, ).

It does seem to be effective for preserving mental performance during physically stressful situations or periods of sleep deprivation when taken in doses ranging from 45–68 mg per pound (100–150 mg per kg) of body weight.

This would be 7–10 grams for a 150-pound (68.2-kg) person.

These higher doses may cause gastrointestinal upset and be split into two separate doses, taken 30 and 60 minutes prior to a stressful event.

Summary Tyrosine as a free-form amino acid is the best form of the supplement. Its greatest anti-stress effects have been observed when it’s taken in doses of 45-68 mg per pound (100–150 mg per kg) of body weight about 60 minutes before a stressful event.